1. Field of the Invention
This invention relates to utility knives used to cut various items, including cartons, cardboard, string and wallpaper. Specifically, my invention provides a disposable one-piece razor blade utility knife in which the blade is adjustable yet permanently affixed to the knife handle. When the complementary shells of the handle are open, the blade may be placed in a usable position in which the cutting edge will protrude out of the handle when the shells of the knife are later closed or the blade may be placed in a safety position in which the blade will be fully retained in the handle when the knife is closed.
2. Description of the Prior Art
Utility knives with adjustable blades are well-known in the art. These utility knives are generally of two types, which share the characteristic of replaceable blades but differ in operation. These utility knives generally are constructed as a pair of complementary shells secured together, forming an enclosure for the knife blade and a frontal opening for the cutting edge of the blade to protrude therethrough.
In one knife structure, the blade is detachably affixed to a separate mounting structure disposed longitudinally within the handle enclosure and extending through the top of the enclosure. Pressure on the exterior mounting moves the blade from its enclosure within the handle to the cutting position. The two shell portions of the handle are generally made of metal and are secured together by screws. Therefore, in order to replace the blade the shells must be unscrewed with a screwdriver.
In another knife structure, the blade is also detachably affixed to a separate mounting structure disposed within the handle so that the blade may be replaced after it has worn out. The mounting structure is attached to one of the shells near the hinge. However, the blade is not moved from one position to another by pressure on an exterior mounting but by the operator when the knife is in an open position. The two shells of the handle are made of plastic and are permanently affixed together along one of the longitudinal sides of each shell and are detachably affixed at the opposite sides, permitting the knife to be open and closed without use of a screwdriver. This arrangement is typified by U.S. Pat. No. 3,520,059 issued to Donald Gringer on July 14, 1970.
Both of the utility knives described above are constructed specifically to permit the user to replace worn-out blades. The blades are not permanently affixed to the handle and thus can easily be loosened when the knives are in use, which can result in a delay in performing the cutting task while the blade is re-secured to the mount.